Dopant-containing polymers having a π-conjugated structure are known to have high conductivity. Dopants are substances to develop conductivity. These polymers are used in antistatic agents, display elements, etc. because of their chemical and physical stability in addition to their high conductivity. They have also been suggested to be used in solid electrolytes for electrolytic capacitors.
One known process of manufacturing such a conductive polymer having a π-conjugated structure is to oxidatively polymerize a monomer with an oxidizing agent in the presence of a dopant. For example, the use of 3,4-ethylenedioxythiophene as a monomer, and a polystyrene sulfonic acid as a dopant results in highly conductive poly3,4-ethylenedioxythiophene doped with the polystyrene sulfonic acid. The poly3,4-ethylenedioxythiophene prepared by this method is in the form of microparticles dispersed in water. Thus, the above-described method can prepare a conductive polymer microparticle dispersion (see, for example, Patent Literature 1).